1. Technical Field
This invention relates to computer system communication; and, more specifically, it relates to an apparatus and method for minimizing nonlinear distortion along computer communication data paths.
2. Description of Related Art
Conventional modems of today are capable of downstream data transfer (server to client) of up to 56,000 bps. The upstream side of the connection (client to server), however, is typically able to transfer data at a maximum rate of only 33,600 bps. Conventional systems utilizing protocols such as the K56Plus(trademark), K56Flex(trademark) and V.90 systems enjoy a digital link on the downstream side of the connection between the Central Office and the client modem. This digital link minimizes the presence of local loop impairments such as linear and non-linear distortion in the transferred signal which make them capable of reaching downstream transfer rates of up to 56,000 bps. The upstream connection, on the other hand, typically utilizes analog modulation of the signal, which, by nature, encounters a greater amount of signal distortion and hence, a reduced transfer rate.
Non-linear distortion is a great impediment to high-speed upstream data transfer in modems of today. With the utilization of standard protocols, such as xcexc-Law and A-Law, Pulse Code Modulation (PCM) encounters difficulties with frequency-specific distortion that cause transmission errors to occur. The transmission errors typically affect the maximum attainable transmission rate significantly. Nonlinear distortions within the upstream data transfer in conventional systems are partially caused by future symbol effects created by impedance echo and reflection. As a signal defining a first symbol travels from the client to the server, another signal defining a second symbol may be leaving the client and heading towards the server, also. The transmission of the second symbol adversely affects the transmission of the first symbol because of echo and reflection phenomena. This inter-symbol effect makes it possible for future symbols to distort the reception of current symbols; thus, introducing error and slowing potential data transfer rates.
Other deficiencies and disadvantages of the prior art will become apparent to one skilled in the art after comparing such prior art with the present invention as described herein.
Various aspects of the present invention may be realized through a server-side equalization system that includes a primary communication channel for transmission of a primary signal, and a secondary communication channel for transmission of a secondary signal. The equalization system also includes a client communication device for sending the primary signal. This client communication device has a pre-equalization module, which modifies the primary signal being sent out, and is communicatively coupled to the primary communication channel. The equalization system further includes a server communication device, which has a linear equalizer communicatively coupled to the primary communication channel, to receive data from the primary communication channel and a sampling module, which is communicatively coupled to the primary communication channel, to sample the primary signal. Lastly, the equalization system includes a non-linear decision feedback equalizer that is communicatively coupled to the secondary communication channel to provide pre-equalization coefficients to the pre-equalization module of the client communication device based on analysis of samples taken from the sampling module. The pre-equalization coefficients are used by the pre-equalization module for correcting non-linear distortions in the primary signal sent upstream to the server communication device.
In one embodiment, the primary communication channel and the secondary communication channel are included in a local loop. In another embodiment, the client communication device is a computer modem. In yet another embodiment, the server communication device is a computer modem. In another alternative, the linear equalizer is utilized with a non-linear decision feedback equalizer to establish a set of equalizer coefficients to be sent by the secondary communication channel to the client modem for updating the pre-equalization module.
In another embodiment, the sampling module is a slicer. In yet another embodiment, the client communication device performs some of the analysis of the samples taken by the sampling device in developing the pre-equalization coefficients. In still another embodiment, the client communication device performs all of the analysis of the samples taken by the sampling device to develop the pre-equalization coefficients for the client communication device. In another embodiment, the client communication device and the server communication device each perform a part of the analysis of the samples to develop pre-equalization coefficients and exchange the pre-equalization coefficients with each other. In yet another embodiment, the client communication device and the server communication device work together in the analysis of the samples taken by the sampling device to develop pre-equalization coefficients for the client communication device. In another embodiment, the pre-equalization module is located in the server communication device and the pre-equalization occurs in the server communication device.
Various aspects of the present invention may also be realized through a communication system that includes a primary communication channel for transmission of a primary signal, and a secondary communication channel for transmission of a secondary signal. The communication system also includes a first communication device, which has a pre-equalization module to modify the primary signal and which is communicatively coupled to the primary communication channel, and a second communication device, which has a first equalizer that is communicatively coupled to the primary communication channel to receive data from the primary communication channel. The communication system further includes a sampling module that is communicatively coupled to the primary communication channel to sample the primary signal and a second equalizer that is communicatively coupled to the secondary communication channel to provide pre-equalization coefficients to the pre-equalization module of the first communication device.
In one embodiment, the first equalizer is a linear equalizer that is utilized with the second equalizer to establish a set of coefficients to be sent by the secondary communication channel to the first modern to update the pre-equalization module. In another embodiment, the second equalizer is a non-linear decision feedback equalizer that has pre-equalization coefficients used by the pre-equalization module for correcting non-linear distortions in the primary signal being sent upstream to the second communication device.
In another embodiment, the first communication device performs part of the analysis of the samples taken by the sampling device to develop the pre-equalization coefficients. In yet another embodiment, the first communication device performs all of the analysis of the samples by itself. In still another embodiment, the first communication device and the second communication device each perform a portion of the analysis of the samples and exchange the pre-equalization coefficients with each other. In another embodiment, the first communication device and the second communication device work together in the analysis of the samples taken by the sampling device to develop the pre-equalization coefficients for the first communication device.
In another embodiment, the pre-equalization module and the pre-equalization process are both located in the second communication. In another embodiment, the first communication device is a client modem. In yet another embodiment, the second communication device is a server modem. In still another embodiment, the first communication device is a server modem. In still another embodiment, the second communication device is a client modem.
Various aspects of the principles according to the present invention may also be realized through a method for performing non-linear equalization. The method comprises identifying, by a first communication system, nonlinear equalization parameters to be used by a second communication system to minimize nonlinear distortions on a primary communication channel. The method also includes transmitting, by the first communication system, the nonlinear equalization parameters to the second communication system by a secondary communication channel. The method further includes receiving, by the second communication system, the nonlinear equalization parameters from the first communication system. Finally, the method includes utilizing, by the second communication system, the nonlinear equalization parameters to minimize nonlinear distortion on the primary communication channel.
In one embodiment of the present invention, the identification of nonlinear equalization parameters includes sampling, by the first communication system, the primary communication channel and calculating, based on the samples, the nonlinear equalization parameters to be used use by the second communication system.